Nanci,

  The experts don't believe at this time that there is a virus or bacteria that remains in the body triggering mast cells.  Some patients feel that their disorder was set in motion by an illness, but the types of illnesses patients report vary from patient to patient.  And, the illness could have been a first mast cell attack that just felt like an infection.  No one knows for sure.  Infections can be degranulation triggers, though, as can anything that revs up the immune system.

  In 2008, Dr. Akin told me that researchers believe the cause of SM  is genetic damage from radiation exposure.  That could be from the atmosphere, earth, reactors, medical exposure or other.  (That doesn't mean we shouldn't have x-rays when we need them.  It would take a lot more exposure to cause this kind of damage.)

  However, there also are cases in which mast cell disorders run in families, which brings up a million other questions that don't have  answers at this time.

  As with any new area of study, of course there could be one or more causes or contributing factors that turn up later.  Research on mast cells is still in a very early stage.